A British parliamentary committee alleges in a doping investigation report that Bradley Wiggins used a banned powerful corticosteroid to enhance his performance while preparing to win the Tour de France in 2012.

The report accuses Team Sky of crossing an "ethical line."

The legislators said they received evidence showing Team Sky sought a therapeutic use exemption for Wiggins to take triamcinolone "to improve his power to weight ratio ahead of the race" in 2012 rather than for medical reasons to treat asthma.

The committee says Wiggins "benefited from the performance enhancing properties of this drug during the race," and raises the prospect of Wiggins' support riders also "possibly" using triamcinolone.

Team Sky criticized "the anonymous and potentially malicious claim". Wiggins denied "any drug was used without medical need."